1. Field of the Invention
The present invention relates generally to the field of semiconductor lasers. More specifically, the present invention relates to single-mode quantum cascade lasers having shaped cavities.
2. Related Art
Quantum cascade (QC) lasers are mid-infrared (mid-IR) laser light sources fabricated from semiconductor (epitaxial) materials. QC lasers are useful in a number different applications, such as molecular detection, environmental trace gas sensing, medical diagnostics, etc. QC lasers are unipolar, and laser emission is achieved through the use of intersubband transitions present in alternating stacks of semiconductor materials.
It is possible to operate QC lasers in so-called “single mode,” wherein the device emits laser light of a single wavelength. Single-mode operation of QC lasers is usually achieved by either integrating distributed feedback (DFB) Bragg gratings into the laser cavity, or by making use of macroscopic gratings in an external cavity (EC) configuration. However, both approaches require complicated fabrication and/or coating processes. EC-QC lasers also require high-precision alignments, therefore the cost for single-mode QC lasers is much higher than that of the simple ridge lasers.
It is known to fabricate QC lasers with resonant waveguides. For example, QC lasers have been fabricated with ridge waveguides such as straight Fabry-Perot (FP) resonators. Such straight FP waveguides/resonators generally operate in multiple longitudinal modes, and therefore are generally not suitable for single-mode applications.